The present invention relates to an electromagnetic valve actuating mechanism.
An electromagnetic valve actuating mechanism of the generic type is disclosed, for example, from German Patent Document DE 694 09 485 T2. The valve actuating mechanism described there has a displaceable control element or an “armature” with an “armature plate”, for actuating a valve of an internal-combustion engine (that is, an intake valve or an exhaust valve). The armature plate is arranged between two solenoids spaced away from one another in the displacement direction. One solenoid is arranged on the side of the armature plate close to the valve, and the other is arranged on the side away from the valve. In addition, two pressure springs are provided, one also being arranged on the side close to the valve, and the other on the side of the armature plate away from the valve. The pressure springs press the control element or the armature plate into a neutral position, in which the spring forces just barely cancel one another out. By energizing one or both solenoids, the control element or the armature plate can be deflected against the spring forces, so that the valve connected with the control element can be opened or closed.
In the neutral position of the control element, the valve is in a “center position”, in which it is partially opened. For the precision adjusting of the neutral position, a hexagonal socket screw is provided which presses against the end of the pressure spring which is away from the valve. The two springs can be prestressed and thus the location of the neutral position of the control element relative to the solenoid can be changed, by rotating the adjusting screw.
Adjustment of the neutral position of the control element requires considerable labor and can be done only in the shop. However, a firmly adjusted neutral position of the control element is always a power-related “compromise” for some operating conditions of the engine. To open or close the valve, one or the other solenoid must be energized. To minimize the demand for electric power, it would be desirable for the neutral position of the control element to be changeable during the operation of the internal-combustion engine.
One object of the invention is to provide an electromagnetic valve actuating mechanism which exhibits an optimized power requirement.
This and other objects and advantages are achieved by the electromagnetic valve actuating mechanism according to the invention, which has an axially displaceable control element with an armature plate, for opening or closing a valve. In addition, two solenoids are provided which are arranged behind one another in the displacement direction and are spaced with respect to one another. One solenoid is arranged on the side of the armature plate close to the valve, and the other is arranged on the side of the armature plate away from the valve. Two springs arranged behind one another in the displacement direction—one on the side of the armature plate close to the valve, and the other on the side away from the valve—press the control element or the armature plate into a neutral position when the solenoids are without current. By energizing the solenoids, the control element or the armature plate can be deflected from the neutral position.
A stop element is provided at one end of the two springs. By adjusting the stop element, the springs can be prestressed, and thus the position of the neutral position of the control element changed with respect to the solenoids.
According to the invention, the stop element is displaceably arranged in the displacement direction of the control element, and an actuating device is provided which permits displacement of the stop element during the operation of the valve actuating mechanism. Thus, the neutral position of the control element can be adjusted during the operation of the engine, as a function of the load condition.
In other words, the neutral position, (in which the forces of the two springs just barely cancel one another out), can be displaced in the direction of the solenoid close to the valve or in the direction of the solenoid away from the valve. Depending on whether the valve is an intake valve or an exhaust valve, it is useful for power-related reasons to change the neutral position of the control element as a function of the loading condition of the internal-combustion engine, during operation.
In the case of the exhaust valve, it is useful, during the start of the engine or in the low-load operation, to bring the control element or the armature plate into a neutral position which corresponds to the center position between the two solenoids. In this neutral position, the armature plate is equally far away from both solenoids if they are not energized. On the other hand, in operation under a load, it is advantageous with respect to the power for the neutral position of the control element to be displaced toward the solenoid close to the valve, which can be done by actuating the actuating element, so that the stop element resting on one spring end can be displaced in the displacement direction of the control element. By displacing the stop element, the prestressing of the two springs, and thus the location of the neutral position, can be changed.
In contrast, in the case of an intake valve, it is advantageous for the control element or the armature plate not to be in the center position between the two solenoids after the engine start or during idling or in the partial-load operation but to be displaced toward the solenoid away from the valve. By actuating the actuating element, the control element can be displaced in the load operation, such that its neutral position corresponds to the center position between the two solenoids.
According to a further embodiment of the invention, a hydraulic actuating device is provided. The actuating device preferably has a swiveling lever with a short and a long lever arm. The short lever arm interacts with the stop element of the actuating device. In contrast, the long lever arm is acted upon by an adjusting force by means of a hydraulic cylinder. The hydraulic cylinder can be connected with the engine oil circulating system by way of a solenoid which can be shut off. In the load operation of the internal-combustion engine, the engine oil pressure is sufficiently high that, when the solenoid is opened, the swiveling arm can be actuated for the adjustment of the neutral position.
Since the required adjusting path of the control element from one neutral position to the other amounts to only a few tenths of a millimeter and the adjusting forces are relatively high, it is expedient to use a swiveling lever with a transmission ratio of 10 to 15 from the long to the short lever arm. By selection of a transmission ratio of from 10 to 15, the high force of the valve spring can be reduced to a lower force level, which can then be applied by the engine oil pressure and a piston with a relatively small piston surface. Such a large transmission ratio also reduces the effects of the tolerances in the piston travel which at an inverse to the transmission ratio have an effect on the neutral position, and thereby simplify the manufacturing of the hydraulic unit.
During actuation of the actuating device, the one end of the upper spring, or the spring away from the valve, is displaced by means of the swiveling lever by twice the amount of the desired neutral position adjustment in the displacement direction.
For precise adjustment of the neutral position, an adjusting screw may be provided at the short lever arm of the swiveling lever. The adjusting screw can be screwed directly into the short lever arm and can press against the stop element of the spring away from the valve. It is preferably secured against rotation by a screw retention device (for example, by means of a lock nut). Such an actuating device can be assigned to a single valve. However, preferably such an actuating device can be provided for adjusting the control elements of two or more valves.
When a hydraulic actuating device is used, the hydraulic pistons assigned to the intake valves or the exhaust valves can be mutually connected by a common oil pipe, and connected to the engine oil circulating system by means of a simple solenoid.
According to a further embodiment of the invention, the actuating device permits a “two-point adjustment”. This means that the control element can be switched between precisely two neutral positions. In this case, no sensor system is required for detecting the location of the neutral position.
Alternatively, a continuous neutral position adjustment may also be provided by means of a corresponding control of the hydraulic pressure. Thus, not only an upper and a lower neutral position can be adjusted, but also arbitrary neutral positions situated in-between.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.